Photopolymerizable composition containing an ethylene terpolymer

ABSTRACT

Mixtures crosslinkable by photopolymerization and based on binders, photopolymerizable monomers compatible therewith and photoinitiators, contain as binders copolymers prepared from (a 1 ) from 30 to 70% by weight of ethylene, (a 2 ) from 5 to 40% by weight of (meth)acrylic acid and (a 3 ) from 5 to 50% by weight of one or more vinyl ester, vinyl ether, (meth)acrylic acid ester and/or (meth)acrylamide.

The present invention relates to mixtures which are crosslinkable byphotopolymerization and based on binders, photopolymerizable monomerscompatible therewith and photoinitiators which contain as binderscopolymers based on ethylene, (meth)acrylic acid and one or more furthercomonomers, and which are suitable for preparing photocrosslinkableprinting plates, relief plates and photoresists and alsophotocrosslinked printing forms, relief forms and photoresists. Thepresent invention also relates to photocrosslinked printing plates,relief plates and photoresists and printing forms, relief forms andphotoresists having improved properties which have been prepared withthe novel mixtures.

Mixtures of this kind are common knowledge and have been frequentlydescribed. However, many of them have disadvantages, such as, forexample, insufficient flexibility, elasticity, storability or chemicalstability, an excessive ozone sensitivity, thermolability orswellability in printing ink solvents or insufficient solubility ordispersibility in liquid polar media. This frequently complicates orprevents use thereof in the preparation of photocrosslinked letterpressor planographic printing forms, relief forms or photoresists.

Mixtures which contain ethylene copolymers are likewise known.

For instance, U.S. Pat. No. 4,010,128 describes flexographic printingforms which for example comprise ethylene/ethyl acrylate copolymers andstyrene-1,3-butadiene-styrene block copolymers. But these are notphotocrosslinkable mixtures; the printing letterpress must beincorporated into these layers by impressing a conventional printingform matrix.

German Laid-Open Application DOS No. 2,548,451 describes a process forpreparing letterpress printing forms made of fiber material, wherein asurface film of, for example, ethylene/vinyl acetate, ethylene/acrylicacid or ethylene-acrylate copolymers is applied to a layer of syntheticfibers by impressing the printing pattern by means of a matrix. In thiscase too the mixtures are not photocrosslinkable.

These mixtures and the forms prepared therefrom are consequently of nohelp in solving the problems which arise in connection with the use ofcustomary photocrosslinkable mixtures.

German Laid-Open Application DOS No. 2,718,047 describes awater-developable photocrosslinkable mixture which contains awater-soluble methacrylic acid polymer. This polymer can also containethylene, although only in an amount of up to 30%, preferably up to 15%,indicated as the ratio of the repeating units in the polymer chain,since otherwise the solubility in water is lost. These mixtures are usedin particular for preparing offset printing forms. The photocrosslinkedforms prepared from these photocrosslinkable mixtures are too hard andtoo brittle for other purposes.

Ethylene copolymers which, in addition to ethylene, also contain two ormore other comonomers are likewise known and are used for a wide varietyof purposes. For instance, British Patent No. 1,386,794 describes theuse of an ethylene copolymer which has from 2 to 40% by weight ofmethacrylic acid and from 5 to 48% by weight of a vinyl ester, alkylacrylate or alkyl methacrylate for preparing steel laminates.

German Laid-Open Application DOS No. 2,359,626 describes a copolymerlatex for preparing adhesives, the copolymer essentially containing from5 to 25% by weight of ethylene, from 0.1 to 10% by weight of(meth)acrylic acid, from 60 to 90% by weight of a vinyl ester and from0.1 to 10% by weight of a hydroxyalkyl acrylate.

German Laid-Open Application DOS No. 2,136,076 recommends copolymers offrom 50 to 93% by weight of ethylene, from 2 to 40% by weight ofmethacrylic acid and from 5 to 48% by weight of a mixture of a vinylester and an alkyl (meth)acrylate for bonding a silicate glass plate toa plastics plate. European Patent No. 115,190 describes ionomerscomprising for example from 10 to 87% by weight of ethylene, from 3 to30% by weight of acrylic acid and from 10 to 60% by weight of an alkylacrylate or of a vinyl ether, whose carboxyl groups are from 3 to 90%neutralized, and the use thereof as coatings for golf balls. The use ofsuch ethylene copolymers in mixtures crosslinkable byphotopolymerization is not known.

It is an object of the present invention to provide novel mixturescrosslinkable by photopolymerization for preparing photocrosslinkableprinting plates, relief plates and photoresists and photocrosslinkedprinting forms, relief forms and photoresists which, in the unexposedstate, are readily soluble or dispersible in liquid polar media and havea high storability and, in the exposed state, have a high solubilitydifferentiation between exposed and unexposed areas, a high flexibility,elasticity, chemical stability, thermostability, abrasion resistance anddimensionl stability, a low swellability in printing ink solvents and inparticular a very low ozone sensitivity. It is a further object of thepresent invention to provide improved photocrosslinkable printingplates, relief plates and photoresists and improved photocrosslinkedprinting forms, relief forms and photoresists.

We have found that these objects are achieved with mixturescrosslinkable by photopolymerization and based on binders,photopolymerizable monomers compatible therewith and photoinitiators,which contain as binders copolymers prepared from (a₁) from 30 to 70, inparticular from 40 to 60% by weight of ethylene, (a₂) from 5 to 40, inparticular from 8 to 30% by weight of (meth)acrylic acid and (a₃) from 5to 50, in particular from 20 to 40% by weight of one or more vinylester, vinyl ether, (meth)acrylic acid ester and/or (meth)acrylamide.

We have also found that these mixtures are highly suitable for preparingphotocrosslinkable printing plates, relief plates and photoresists andphotocrosslinked printing forms, relief forms and photoresists. We havefurther found photocrosslinkable printing plates, relief plates andphotoresists and photocrosslinked printing forms, relief forms andphotoresists of high elastomeric properties and ozone stability whichwere prepared using these mixtures.

Said plates, forms and photoresists are referred to hereinafter, forshort, as "light-sensitive recording materials".

For the purposes of the present invention, the term liquid polar mediarefers to such solvents, solvent mixtures or mixtures of solvents andadditives as have a high dipole moment and/or ionic charges andtherefore are capable of entering dipole-dipole, dipole-ion or ion-ioninteractions with themselves or with other compounds. The term liquidpolar media also includes such solvents, solvent mixtures or mixtures ofsolvents and additives as have the aforementioned properties andadditionally possess loosely bonded protons or hydroxyl ions.

In the light of the cited prior art, it was surprising and notforeseeable that the copolymers to be employed according to theinvention can be used to prepare mixtures crosslinkable byphotopolymerization which are elastomeric and, despite their highethylene content, soluble or at least readily dispersible in liquidpolar media and also stable to ozone and which for that reason are veryhighly suitable for preparing light-sensitive recording materials. Thesein turn have surprising advantages. For instance, in the unexposed statethey are storable, dimensionally stable and nontacky. After imagewiseexposure with actinic light, they exhibit excellent solubilitydifferentiation between their exposed and unexposed areas, so that theyare simple to develop by means of liquid polar, and in particularaqueous, media. The developed light-sensitive recording materials,furthermore, are so flexible that they can be repeatedly clamped ontosmall printing cylinders. In addition, they undergo little swelling, ifany, in aqueous printing inks; they are dimensionally stable andabrasion-resistant and, moreover, stable to ozone. Even with long printruns, they thus permit very good image reproduction which is exact andfaithful even in the finest details. The recording materials accordingto the invention additionally have other significant and importantapplication advantages compared with the prior art, for example bettershadow well depth in screened halftone areas and negative lines.

The binder copolymers of a₁ ethylene, a₂ (meth)acrylic acid and a₃ oneor more vinyl ester, vinyl ether, (meth)acrylic acid ester and/or(meth)acrylamide are known per se. They are prepared by the LDPE (lowdensity polyethylene) high-pressure polymerization method at 200°-400°C. under more than 800 kg/cm² [see for example German Patent No.2,341,462, U.S. Pat. No. 3,264,272 and German Patent Application P No.35 39 469.2 (O.Z. 38087)].

Vinyl esters suitable for use as comonomers a³ are in particular thoseof the general structure (I) ##STR1## where R is alkyl or cycloalkyl of1 to 10 carbon atoms, for example vinyl acetate, vinyl propionate, vinylbutyrate, vinyl valerate or vinyl hexanoate, of which vinyl acetate ispreferred.

Vinyl ethers suitable for use as comonomers a₃ are in particular thoseof the structure (II)

    CH.sub.2 =CH--OR                                           (II)

for example vinyl ethyl ether, vinyl 1-propyl ether, vinyl 1-butylether, vinyl 2-butyl ether or vinyl 1-pentyl ether, of which vinyl1-butyl ether is preferred.

(Meth)acrylic acid esters and (meth)acrylamides suitable for use ascomonomers a³ are in particular those of the structure (III) ##STR2##where R¹ is hydrogen or methyl, Z is oxygen or an NR³ group (with R³ =Hor C₁ -C₄ -alkyl) and R² is alkyl or cycloalkyl of 1 to 10 carbon atomsor ω-alkyl-poly(alkylene oxide)-α-oxyl. Suitable (meth)acrylic acidesters and amides are for example methyl acrylate, methyl methacrylate,ethyl acrylate, ethyl methacrylate, propyl acrylate, propylmethacrylate, n-butyl acrylate, n-butyl methacrylate, n-pentyl acrylate,n-pentyl methacrylate, n-hexyl acrylate, n-hexyl methacrylate,tert.-butyl acrylate, cyclohexyl acrylate, cyclohexyl methacrylate,2ethylhexyl acrylate, 2-ethylhexyl methacrylate, dicyclopentadienylacrylate, ω-methyl-poly(ethylene oxide)-α-yl (meth)acrylate,ω-methyl-poly(propylene 1,2-oxide)-α-yl (meth)acrylate,ω-methyl-poly(propylene 1,3-oxide)-α-yl (meth)acrylate,N-ethylacrylamide, N-methyl-N-butylmethacrylamide orN-ethyl-N-(2-ethylhexyl)-acrylamide. Preference is given to n-butylacrylate, 2-ethylhexyl acrylate, ω-methyl-poly(ethylene oxide)-α-ylacrylate and dicyclopentadienyl acrylate, of which the first three areparticularly preferred.

Preferred binders are accordingly ethylene/(meth)acrylic acid copolymerswhich contain n-butyl acrylate, 2-ethylhexyl acrylate and/orΩ-methyl-poly(ethylene oxide)-α-yl acrylate as copolymerized comonomersa₃ and have a Shore A hardness of greater than 10, in particular from 15to 75. The copolymers to be employed according to the invention are usedin an amount of from 30 to 99.5, advantageously from 40 to 96,preferably from 50 to 93, and in particular from 60 to 90% by weight,based on a mixture according to the invention.

Suitable photopolymerizable monomers are nongaseous and must be capableof forming a high polymer via a free radical initiated chain propagationreaction and addition polymerization and also be compatible with thebinders according to the invention. Compatible is to be understood hereas meaning the ability of two or more constituents to remain dispersedin one another.

A class of suitable photopolymerizable monomers comprises theunsaturated esters of alcohols, in particular esters ofα-methylenecarboxylic acids and substituted α-methylenecarboxylic acids,in particular esters of this kind with alkylenepolyols andpolyalkylenepolyols, of which alkylenepolyol di- and triacrylates andpolyalkylenepolyol di- and triacrylates which have been prepared fromalkylenepolyols of 2 to 15 carbon atoms or polyalkylene ether polyols orglycols having 1 to 10 ether bonds are particularly preferred.

The following specific compounds illustrate further suitable monomers:ethylene glycol diacrylate, diethylene glycol diacrylate, glyceroldiacrylate, glycerol triacrylate, trimethylolpropane triacrylate,ethylene glycol dimethacrylate, 1,3-propanediol dimethacrylate,1,2,4-butanetriol trimethacrylate, 1,4-cyclohexanediol diacrylate,1,4-benzenediol dimethacrylate, 1,2-benzenedimethanol diacrylate,pentaerythritol triacrylate, pentaerythritol tetramethacrylate,1,3-propanediol diacrylate, 1,3-pentanediol dimethacrylate,p-α,α-dimethylbenzylphenyl acrylate, tert.-butyl acrylate,N,N-diethylaminoethyl acrylate, N,N-diethylaminoethyl methacrylate,1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, 1,6-hexanedioldimethacrylate, 1,10-decanediol diacrylate, 2,2-dimethylolpropanediacrylate, tripropylene glycol diacrylate,2,2-di(p-hydroxyphenyl)propane diacrylate,2,2-di(p-hydroxyphenyl)propane dimethacrylate,polyoxyethyl-2,2-di(p-hydroxyphenyl)propane dimethacrylate,polyoxypropyltrimethylolpropane triacrylate (molecular weight 462),1,4-butanediol dimethacrylate, 1,6-hexanediol methacrylate,2,2,4-trimethyl-1,3-pentanediol dimethacrylate,1-phenylethylene-1,2-diol dimethacrylate, trimethylolpropanedi(meth)acrylate, triethylene glycol diacrylate, tetramethylene glycoldiacrylate, ethylene glycol acrylate phthalate,polyoxyethyltrimethylolpropane triacrylate, diacrylate anddimethacrylate esters of diepoxypolyethers which have been derived fromaromatic polyhydroxy compounds, for example bisphenols, novolaks andsimilar compounds, such as, for example, the compounds described in U.S.Pat. No. 3,661,576, and the bisacrylates and bismethacrylates ofpolyethylene glycols of molecular weight 200 to 500 and the like.However, it is also possible to use alkylpolyalkylene oxidemono(meth)acrylates, for example ω-methyl-poly(ethylene oxide)-α-ylacrylate. Also suitable are reaction products of glycerol,epichlorohydrin and acrylic acid in a molar ratio of, for example,1:3:3.

A further class of suitable monomers is formed by the compoundsdescribed in U.S. Pat. No. 2,927,022, for example compounds having aplurality of olefinic bonds which are polymerizable by polyaddition, inparticular if they are present as terminal bonds, in particularcompounds in which at least one and preferably most of these bonds areconjugated with a double-bonded carbon, including carbon which isdouble-bonded to carbon and heteroatoms such as nitrogen, oxygen andsulfur. Preference is given to compounds in which the ethylenicallyunsaturated groups, in particular the vinylidene groups, are conjugatedwith ester or amide structures. Specific examples of such compounds arethe unsaturated amides, in particular those with α-methylenecarboxylicacids, ω-diamines and ω-diamines which are interrupted by oxygen, forexample methylenebisacrylamide, methylenebismethacrylamide,ethylenebismethacrylamide, 1,6-hexamethylenebisacrylamide,diethylenetriaminetrismethacrylamide,bis(γ-methacrylamidopropoxy)-ethane, β-methacrylamidoethyl methacrylate,N-(β-methacryloxyethyl)-acrylamide, vinyl esters, for example divinylsuccinate, divinyl adipate, divinyl phthalate, divinyl terephthalate,divinyl benzene-1,3-disulfonate and divinyl butane 1,4-disulfonate anddiallyl fumarate.

Further suitable monomers are: styrene and styrene derivatives,1,4-diisopropenylbenzene, 1,3,5-triisopropenylbenzene, adducts ofitaconic anhydride with hydroxyethyl acrylate (1:1), with liquidbutadiene-acrylonitrile polymers which contain terminal amino groups,and adducts of itaconic anhydride with diacrylates and dimethacrylatesof diepoxypolyethers which are described in U.S. Pat. No. 3,661,576,polybutadiene and butadieneacrylonitrile copolymers with terminal andlateral vinyl groups and unsaturated aldehydes, for example sorbaldehyde(2,4-hexadienal).

Suitable monomers which are water-soluble or contain carboxyl groups orother groups capable of reaction with alkali are particularly highlysuitable if the material is to be developable with aqueous media. It isalso possible to use the polymerizable, olefinically unsaturatedpolymers and similar materials mentioned in U.S. Pat. Nos. 3,043,805 and2,929,710 alone or as a mixture with other materials. Acrylic acidesters and methacrylic acid esters of adducts of ethylene oxide andpolyhydroxy compounds as described in U.S. Pat. No. 3,380,831 arelikewise suitable.

When carboxyl-containing monomers are used, the carboxyl groups can bewholly or partly neutralized with metal hydroxides, carbonates and thelike or with inorganic and organic nitrogen bases such as ammonia ortriethylamine.

In general, the suitable photopolymerizable monomers are used in anamount of from 1 to 40, in particular from 5 to 30% by weight, based ona mixture according to the invention.

Preference is given to trimethylolpropane triacrylate, 1,6-hexanedioldiacrylate, 1,6-hexanediol dimethacrylate, ω-methyl-poly(ethyleneoxide)-α-yl acrylate and tetraethylene glycol diacrylate.

Suitable photoinitiators which are to be used on their own or as amixture with one another are for example acyloins and derivativesthereof, such as benzoin, benzoin alkyl ethers, for example benzoinisopropyl ether, α-methylolbenzoin and ethers thereof, for exampleα-methylolbenzoin methyl ether, or α-methylbenzoin and α-methylbenzoinethyl ether; vicinal diketones and derivatives thereof, for examplebenzil, benzil acetals, such as benzil dimethyl acetal, benzil methylethyl acetal, benzil methyl benzyl acetal or benzil ethyleneglycolacetal; and also in particular acylphosphine oxide compounds of the typedescribed for example in DE-A-No. 29 09 992 and DE-A-No. 31 14 341 foruse in photopolymerizable mixtures. Preferred representatives ofinitiators from the class of the acylphosphine oxides are2,6-dimethoxybenzoyldiphenylphosphine oxide,2,4,6-trimethylbenzoyldiphenylphosphine oxide, ethyl2,4,6-trimethylbenzoylphenylphosphinate and sodium2,4,6-trimethylbenzoylphenylphosphinate. The photoinitiators can also beused in combination with other coinitiators and/or activators asdescribed in the relevant literature. Also suitable, however, arephotoreactive initiators which initiate a cationic polymerization, suchas the pyrrylium hexafluoroarsenates described in European Patent No.74,073. Preference is given to benzil dimethyl acetal and/or2,4,6-trimethylbenzoyldiphenylphosphine oxide. oxide.

In general, suitable photoinitiators are used in an amount of from 0.001to 10, preferably from 0.1 to 8 and in particular 0.1 to 3% by weight,based on a mixture according to the invention.

The mixtures according to the invention can further contain suitablenonphotopolymerizable or nonphotocrosslinkable aids and/or additives.These include, for example, inhibitors of thermally initiatedpolymerization, processing aids and plasticizers, dyes and pigments andalso salifiers, i.e. cation-donating substances.

Suitable inhibitors of thermally initiated polymerization are forexample hydroquinone, hydroquinone derivatives,2,6-di-tert.-butyl-p-cresol, nitrophenols, N-nitrosamines, such asN-nitrosodiphenylamine or the salts, in particular the alkali metal,calcium and aluminum salts, of N-nitrosocyclohexylhydroxylamine.Preference is given to 2,6-di-tert.-butyl-p-cresol and the alkali metalsalts of N-nitrosocyclohexylhydroxylamine. In general they are used inamounts of from 0.001 to 5% by weight, based on a mixture according tothe invention.

Examples of suitable processing aids and plasticizers are dialkylphthalates, alkyl phosphates, sulfonamides, poly-ethylene glycol, andpolyethylene glycol esters and ethers. It is also possible to useamphiphiles based on polyethylene glycol/fatty acids or polyethyleneglycol/polypropylene oxide block copolymers. In general they are used inan amount of from 1 to 20% by weight, based on a mixture according tothe invention.

Suitable dyes are in particular the soluble phenazinium, phenoxazinium,acridinium and phenothiazinium dyes, e.g. neutral red (C.I. 50,040),safranine T (C.I. 50,240), rhodanil blue, the salt or amide of rhodamineD (Basic Violet 10, C.I. 45,170), methylene blue (C.I. 52,015), thionine(C.I. 52,025) and acridine orange (C.I. 46,005); or even Sudan deepblack X 60 (C.I. 26,150). These dyes, which can in general be added inamounts of from 0.0001 to 2% by weight, based on a mixture according tothe invention, are advantageously used together with a sufficient amountof a reducing agent which does not reduce the dye in the absence ofactinic light, but which, on exposure to light, can reduce the dye inthe excited state. Examples of such mild reducing agents are ascorbicacid, anethole, thiourea and derivatives thereof, such asdiethylallylthiourea and in particular N-allylthiourea, and alsohydroxylamine derivatives, preferably salts ofN-nitrosocyclohexylhydroxylamine, in particular the potassium, calciumand aluminum salts. The latter can also be used as inhibitors tothermally initiated polymerization. The amount of added reducing agentcn in general be from about 0.005 to 5% by weight, in particular from0.01 to 1% by weight, based on a mixture according to the invention, inmany cases the addition of from 3 to 10 times the amount of the dyehaving proved advantageous.

Suitable salifiers are

1. inorganic metal compounds such as oxides, hydroxides, alkoxides wherealkyl is of 1 to 4 carbon atoms or carbonates of the cations of Li, Mg,Ca, Sr, Ba, Al, Ga, In, Ge, Sn, Pb, Sb, Bi, Zn, Cd, Mg, Cn, Sc, Y, La,Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Co, Ni, Pd or thelanthanides or

2. organic metal compounds of the structure (IV) ##STR3## where Me is acation of one of the aforementioned elements, R⁴, R⁵ and R⁶ are each thesame or a different kind of alkyl, cycloalkyl, aryl or alkylaryl, itbeing possible for R⁴ and R⁶ to be bonded to each other cyclically viaring systems, and where R⁵ can also be hydrogen,

3. polyfunctional amines such as ethylenediamine, diethylenetriamine,N-methyl-N-ethylethylenediamine, N,N-dimethylethylenediamine,N,N'-diethylethylenediamine, N,N,N',N'-tetramethylethylenediamine,N,N,N",N"-tetramethylethylenetriamine, 1,3-diaminopropane,1,4-diaminobutane, pyrazine or polyvinylpyridine or

4. hydrazine.

Preference is given to the oxides, hydroxides, alkoxides, carbonates andacetylacetonates of Li⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Al³⁺, Sn²⁺, Sb³⁺ andZn²⁺, of which bis(acetylacetonato)-Zn(II), MgO and LiOH areparticularly preferred.

They can be used in an amount of from 0.05 to 20, preferably from 0.5 to15 and in particular from 1 to 10% by weight, based on a copolymer to beemployed according to the invention.

Further aids and additives are agents for improving the reliefstructure, for example 9,9'-dianthronyl and 10,10'-bisanthrone asdescribed in German Laid-Open Application DOS No. 2,720,560.

All these components of the mixtures crosslinkable byphotopolymerization, or of the light-sensitive recording materials, haveto be adapted to one another in such a way that, after imagewiseexposure with actinic light, the light-sensitive recording materials canbe washed out, i.e. are developable, with liquid polar media. Examplesof liquid polar media which can be used are diethyl ether, di-n-butylether, ethyl butyl ether, tetrahydrofuran, dioxane, acetone, methylethyl ketone, methyl butyl ketone, acetonitrile, propionitrile,acetylacetone, ethyl acetylacetate, pyridine, pyrrole, pyrazine,chloroform, water, methanol, ethanol, propanol, n-butanol, ethanolamine,diethanolamine, triethanolamine, acetic acid or propionic acid andmixtures thereof, if miscible. They can also contain additives, forexample ammonia, amines, metal hydroxides, organic and inorganic acids,organic and inorganic salts and also organic compounds. Preference isgiven to an 0.5% strength alkali metal hydroxide solution in water,water containing 0.5% by weight of alkali metal hydroxide and 0.01% byweight of sodium paraffinsulfonate of 12 to 18 carbons in thehydrocarbon chain, and a mixture of tetrachloroethylene and n-butanol ina volume ratio of 4:1.

The preparation, from the components mentioned, of the novel mixturescrosslinkable by photopolymerization has no special methodologicalfeatures, but can be effected in a suitable manner by kneading, mixingand dissolving techniques.

To prepare light-sensitive recording materials, the mixtures accordingto the invention can then be shaped into sheetlike structures of varyingthickness in a suitable manner, for example by casting from solution,hot pressing, calendering or extruding. These sheetlike structures areused as light-sensitive recording materials either as such or bonded toother sheetlike materials. In what follows, the sheetlike structures arereferred to as relief-forming layer (RL). Recording materials which havea relief-forming layer (RL) combined with other sheetlike materials arereferred to hereinafter as multilayer elements.

The thickness of the relief-forming layer (RL) can vary within widelimits, depending on the use intended for the light-sensitive recordingmaterials, and will in general be within the range from 0.1 to 6000 μm.Preferred thicknesses for preparing letterpress forms, relief forms andphotoresists are within the range 20 to 6500 μm and for preparingplanographic printing forms within the range from 1 to 200 μm.

Suitable bases (B) in such multilayer elements are the dimensionallystable, rigid or flexible bases customary and known for preparingprinting forms, relief forms or photoresist patterns. They include inparticular dimensionally stable plastics films, for example polyesterfilms, elastomeric films or foams and also metallic bases, for examplesteel, iron , nickel or aluminum sheets or conical nickel sleeves. Toprepare photoresist layers, it is also possible to use copper,copper-coated materials, printed circuits etc. as base materials for therelief-forming layers (RL). The bases (B), in particular those made ofmetal, can be pretreated in a conventional manner mechanically,chemically, electrochemically and/or by priming. To obtain sufficientadhesion between base (B) and relief-forming layer (RL), one or more,generally from 0.4 to 40 μm thick, adhesive layers can be arrangedbetween the base (B) and the relief-forming layer (RL), in particular inthe case of multilayer elements for the preparation of printing andrelief forms. The choice of base material depends chiefly on theproposed use of the multilayer elements. The adhesive layer between base(B) and relief-forming layer (RL) can be made for example of knownpolyurethane-based one- or two-component adhesives or adhesive layers asdescribed in German Laid-Open Application DOS No. 3,015,419.

The relief-forming layer (RL) of the multilayer elements canadditionally be covered with one or more bright or matt cover sheetand/or protective cover sheet which, for example, comprises polyvinylalcohol having a high degree of hydrolysis or mixtures of polyvinylalcohol with the copolymers to be employed according to the invention.Also possible, however, are protective and/or cover films made ofpolystyrene, polyethylene, polypropylene or polyethylene terephthalatewhich can be peeled off the relief-forming layer (RL) after or beforeimagewise exposure with actinic light. A protective and/or cover sheetand a corresponding peel-off film can be used together, the cover sheetand/or protective cover sheet being directly in contact with therelief-forming layer (RL) and staying firmly bonded thereto as the filmis peeled off. Between the cover sheet and/or protective cover sheet andthe corresponding film there may additionally be present an antiadhesivecoating as described in European Patent No. 68,599. The cover and/orprotective cover sheets and films and also the base (B) can containantihalation agents.

The light-sensitive recording materials and multilayer elements aresuitable for example for preparing planographic printing forms orphotoresists as used for example in the manufacture of printed circuits,integrated circuits, in semiconductor technology, in etching etc. andalso for preparing relief structures. They are particularly suitable,however, for preparing flexographic and letterpress printing forms,including in the case of the latter jobbing forms. To this end, therelief-forming layer (RL) of the light-sensitive recording materials orthe multilayer elements is exposed imagewise in a conventional mannerwith actinic light and developed with liquid polar media by washing outthe unexposed, uncrosslinked areas of the layer.

Exposure, which can take the form of flat-plate or rotary exposure, canbe effected with the conventional sources of actinic light, for exampleUV fluorescence tubes, mercury high-, medium- or low-pressure lamps,superactinic luminescent tubes, xenon pulsed lamps, metal halide-dopedlamps, carbon arc lamps etc. The emitted wavelength should in general befrom 230 to 450 nm, preferably from 300 to 420 nm, and be adapted to theself-absorption of the photoinitiator used.

The relief image can be developed by washing, brushing etc. with thepolar developer solvent. Owing to the high water stability of theexposed relief-forming layer (RL), the recording materials andmultilayer elements have the advantage that the washout conditionsduring development can be intensified without impairing the printingforms, relief forms or photoresist patterns. On the contrary, crisperrelief structures are obtained as a result. After the washout, theresulting printing forms, relief forms or photoresist patterns are driedin a conventional manner, if dsired at temperatures up to 120° C. . Insome cases it is expedient subsequently to subject the printing forms,relief forms or photoresist patterns obtained once more to uniformexposure with actinic light to increase the strength of the relieflayer.

These light-sensitive recording materials, which are prepared using themixtures according to the invention, result not only in printing forms,relief forms and photoresist patterns having an extremely high waterstability, so that they have a long shelf life and high degree ofreusability even in a moist warm atmosphere, but also in products ofbetter shadow depths and better crispness than the conventional systems,of pronounced relief structure, high elasticity and smooth surface.

The invention is explained by the Examples below. The parts andpercentages in the Examples are by weight, unless otherwise stated.Parts by volume relate to parts by weight as the liter relates to thekilogram.

The Examples according to the invention involved a number of copolymersprepared as described in German Patent No. 2,341,462, U.S. Pat. No.3,264,272 or German patent application P No. 35 39 469.2 (O.Z. 38087).Their compositicn is shown in Table 1 and important applicationproperties in Table 2.

The Shore A hardness was determined in accordance with DIN 53,505. Themelt flow index (MFI) was measured at 160° C. under a force of 325 p orat 190° C. under a force of 2.16 kp. The ozone stability of therecording materials was determined at 25° C. at an ozone concentrationof 50 ppm on 10 cm long samples which had been subjected to anelongation of 10%; the criterion was whether cracks appeared within 10hours. The swelling in % by weight was determined after 24 hours ofsubmersion in water at 25° C.

                  TABLE 1                                                         ______________________________________                                        Composition of the copolymers                                                 Copolymer/   Content of copolymerized monomers (%)                            monomers     1       2       3     4     5                                    ______________________________________                                        Ethylene     53.8    43.9    57.1  51.6  52                                   Acrylic acid 9.2     19.2    18.9  14.4  17                                   n-Butyl acrylate                                                                           37      37      24    --    19                                   ω-Methyl-poly-                                                                       --      --      --    24    12                                   (ethylene oxide)-α-                                                     yl acrylate                                                                   2-Ethylhexyl --      --      --    10    --                                   acrylate                                                                      ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Properties of the copolymers                                                  Copolymer/                                                                    property    1        2       3     4     5                                    ______________________________________                                        MFI*        200.sup.2                                                                              .sup. 15.sup.1                                                                        .sup. 48.sup.2                                                                      .sup. 28.sup.1                                                                      .sup. 15.sup.1                       Shore A hardness                                                                          21       14      40    35    22                                   ______________________________________                                         *MFI = melt flow index;                                                       .sup.1 160° C./325 p;                                                  .sup.2 190° C./2.16 kp;                                           

Preparation of mixtures crosslinkable by photopolymerization and oflight-sensitive recording materials and multilayer elements EXAMPLE 1

A mixture was prepared from the following components:

76.494% of copolymer 2 as per Table 1,

10% of trimethylolpropane triacrylate,

10% of tetraethylene glycol diacrylate,

3% of benzil dimethyl acetal

0.5% of 2,6-di-tert.-butyl-p-cresol and

0.006% of Sudan Deep Black X 60 (C.I. 26,150).

The components were dissolved in a solvent mixture of toluene and methylethyl ketone in a volume ratio of 1:1, and the end concentration of thesolution was adjusted with the solvent mixture to 28%, based on thetotal weight of the solution. The solution was cast onto a 125 μm thickpolyethylene terephthalate film so that a dry thickness of 1000 μmresulted. After laminating with a 9 μm thick polyester film, thismultilayer element was exposed for 25 minutes through a negativeoriginal. The 9 μm thick polyester film was then removed, and theexposed layer was developed for 20 minutes in 0.5% strength aqueoussodium hydroxide solution with a brush washer. Drying gave a reliefimage having a relief depth of 700 μm and corresponding to thetransparent areas of the negative. The swelling after 24 hours ofsubmersion in water at 20° C. was only 0.6% by weight. The resilient andflexible plate had a nontacky surface and excellent image resolution.Even after prolonged storage there were no ozone cracks in the surface.The resilient and flexible plate was capable of repeated clamping to asmall printing cylinder without problems and gave very good printingresults even after repeated use.

EXAMPLE 2

A mixture and a multilayer element were prepared as in Example 1 from

86.5% of copolymer 3 as per Table 1, 6.3% of 1.6-hexanediol diacrylate,

3.7% of 1,6-hexanediol dimethacrylate,

3% of benzil dimethyl acetyl and

0.5% of 2,6-di-tert.-butyl-p-cresol.

The multilayer element was exposed for 20 minutes through a negativeoriginal and developed for 30 minutes at 40° C. in 0.5% strength aqueouspotassium hydroxide solution with a brush washer. Drying gave a platehaving a Shore A hardness of 63 and a relief depth of 700 μm and alsoexcellent application properties.

EXAMPLE 3

A mixture was prepared from:

85% of copolymer 4 as per Table 1,

10% of trimethylolpropane triacrylate,

3% of benzil dimethyl acetal and

2% of 2,6-di-tert.-butyl-p-cresol

by kneading for 20 minutes at 120° C. in a plastograph, by firstplasticizing the binder and then adding a mixture of monomer, initiatorand inhibitor. The result obtained was a transparent, tacky mass, whichwas hot-pressed at 120° C. between a steel base and a polyester film toa thickness of 1250 μm. After cooling down, this multilayer element wasexposed imagewise for 10 minutes and, after removal of the polyesterfilm, developed with a brush washer in 0.5% strength aqueous sodiumhydroxide solution which contained 0.01% of sodium paraffinsulfonate.Drying left a relief layer having a relief depth of 800 μm and ahardness of 61 Shore A.

EXAMPLE 4

A mixture was prepared in a twin-screw extruder by extruding

82.994% of copolymer 5 as per Table 1, stabilized with2,6-di-tert.-butyl-p-cresol,

10% of ω-methyl-poly(ethylene oxide)-α-yl acrylate,

5.0% of trimethylolpropane triacrylate,

2.0% of benzil dimethyl acetal and

0.006% of Sudan Deep Black X 60 (C.I. 26,150)

In detail, copolymer 5 was introduced into the extruder at a uniformrate by way of a screw conveyor, and melted at 140° C. . The othercomponents were pumped into the extruder in succession, and the mixturewas discharged through a broad-slot die. A calender roll was used toprepare a 3000 μm thick relief-forming layer between a 125 μm thickpolyester film and a 3 μm thick polyvinyl alcohol substrate. Thismultilayer element was preexposed for 3 minutes through the polyesterfilm and then fully exposed for 20 minutes through a negative originalplaced on top of the polyvinyl alcohol substrate. After removal of thenegative original, the recording material was divided and developed (a)with 0.5% strength aqueous sodium hydroxide solution at 50° C. in abrush washer and (b) with tetrachloroethylene/n-butanol (volume ratio4:1) in a spray washer. Both developments gave plates having a reliefdepth of 1000 μm and a Shore A hardness of from 48 to 50. The swellingin water was less than 5% by weight. Both the plates wereozone-resistant and capable of repeated clamping onto small printingcylinders without breaking.

EXAMPLE 5

A mixture was prepared as described in Example 1 from

88% of copolymer 1 as per Table 1,

6.7% of 1,6-hexanediol diacrylate,

3.3% of 1,6-hexanediol dimethacrylate and

2% of benzil dimethyl acetal.

The solution was cast onto a 300 μm thick steel sheet so that a drythickness of 1600 μm resulted. After laminating with a 9 μm thickpolyester film this multilayer element was exposed for 15 minutesthrough a negative original. The film was then removed, and the elementwas developed for 6 minutes with a mixture oftetrachloroethylene/n-butanol (volume ratio 4:1). Drying gave a platehaving good image resolution, a relief depth of 600 μm and a Shore Ahardness of 44.

We claim:
 1. A photopolymerizable mixture comprising(A) from 40 to 96%by weight, based on the mixture, of one or more copolymer bindersconsisting of(a₁) from 30 to 70% by weight of ethylene, (a₂) from 5 to40% by weight of acrylic acid or methacylic acid, and (a₃) from 5 to 50%by weight of one or more comonomers selected from the group consistingof vinyl esters of the strucutre (I), ##STR4## where R is alkyl orcycloalkyl or 1 to 10 carbon atoms, vinyl ethers, acrylic acid esters,methacrylic acid esters, acrylamides and methacrylamides, (B) from 1 to40% by weight, based on the mixture, of one or more nongaseous,photopolymerizable, ethylenically unsaturated monomers which arecompatible with said binders (A), and (C) from 0.001 to 10% by weight,based on the mixture, of one or more photoinitiators.
 2. Thephotopolymerizable mixture of claim 1 further comprising(D) from 0.001to 5% by weight, based on the mixture, of one or more inhibitors ofthermally initiated polymerization, (E) from 1 to 20% by weight, basedon the mixture, of processing aids and plasticizers, (F) from 0.0001 to2% by weight, based on the mixture, of a dye.
 3. The photopolymerizablemixture of claim 2 further comprising(G) from 0.005 to 5% by weight,based on the mixture, of a reducing agent.
 4. The photopolymerizablemixture of claim 1 wherein the copolymer binders (A) consist of(a₁) from40 to 60% by weight of ethylene, (a₂) from 8 to 30% by weight of acrylicacid or methacrylic acid, and (a₃) from 20 to 40% by weight of one ormore comonomers selected from the group consisting of vinyl esters ofthe strucuture (I) ##STR5## where R is alkyl or cycloalkyl of 1 to 10carbon atoms, vinyl ethers, acrylic acid esters, methacrylic acidesters, acrylamides and methacrylamide.
 5. The photopolymerizablemixture of claim 1 wherein the nongaseous, photopolymerizable,ethylenically unsaturated monomers (B) are selected from the groupconsisting of trimethylolpropane triacylate, 1,6-hexanediol diacrylate,1,6-hexanediol dimethacrylate, ω-methyl-poly(ethylene oxide)-α-ylacrylate and tetraethylene glycol diacrylate.
 6. The photopolymerizablemixture of claim 1 wherein the comonomers (a₃) are acrylic acid estersselected from the group consisting on n-butyl acrylate, 2-ethylhexylacrylate and ω-methyl-poly(ethylene oxide)-α-yl acrylate.
 7. Thephotopolymerizable mixture of claim 5 wherein the comonomers (a₃) areacrylic acid esters selected from the group consisting of n-butylacrylate, 2-ethylhexyl acrylate and ω-methyl-poly(ethylene oxide)-α-ylacrylate.
 8. The photopolymerizable mixture of claim 1 wherein thephotopolymerizable, ethylenically unsaturated monomers (B) are selectedfrom the group consisting of trimethylolpropane triacrylate,1,6-hexandiol diacrylate, 1,6-hexanediol dimethacrylate,ω-methyl-poly(ethylene oxide)α-yl acrylate and tetraethylene glycoldiacrylate.
 9. The photopolymerizable mixture of claim 3 wherein thecomonomer (a₃) are acrylic acid esters selected from the groupconsisting of n-butyl acrylate, 2-ethylhexyl acrylate andω-methyl-poly(ethylene oxide)-α-yl acrylate.